<html>
<head>
<style type="text/css">
#openclose
{
z-index: 1;
}
#abc
{
z-index: -1;
}
</style>
<script type="text/javascript" src="a.js"></script>
</head>
<body>
<p>
<a href="javascript://" onclick="calendar('abc')"><img id="openclose" src="open_plus.gif" alt="open" title="open" style="border: none; width: 45px; height: 45px;" /></a>
</p>
<div id="abc">a</div>
</body>
</html>